Buoyancy engines are in widespread use in submersible vehicles and objects such as underwater gliders or underwater drones. Buoyancy engines cause a change of volume displacement, thus vehicle density change. The volumetric change is usually done by either an electric actuator, compressed gas or by the thermodynamic change of a material. Electric actuators, although efficient within deeper waters, still require non-rechargeable lithium batteries to maintain high-endurance and thus are very costly due to frequent battery replacement. Moreover, lithium-ion batteries are very dense, requiring the submersible vehicle to compensate with empty volume to maintain neutral buoyancy underwater. Other conventional buoyancy control systems utilize compressed air. Although compressed air has specific energy and density that are significantly lower than that of lithium-ion batteries, such systems require onboard air compressors and electrical energy storage devices to power the onboard air compressors. Thus, for endurance missions, buoyancy control systems using compressed air are actually inferior to buoyancy control systems using electric actuators. Another conventional buoyancy control system is the thermal powered buoyancy engine which is used in the Slocum Thermal Glider. However, thermal powered buoyancy engines rely only on the temperature change caused by the thermocline ocean layer. Thus, such thermal powered buoyancy engines restrict the submersible vehicle's depth and/or location of operation.
What is needed is a new and improved buoyancy control system for submersible objects that eliminates the problems and disadvantages associated with conventional buoyancy control systems.